1. Field of the Invention
The present invention relates to a semiconductor device and a control method in a semiconductor device, and more particularly to a semiconductor device in which information will not be analyzed even if an analyzer is connected.
2. Description of the Related Art
Recently leakage and the theft of personal information and confidential information are becoming problems in such information terminal devices as notebook type personal computers and PDAs (Personal Digital Assistants). Such personal and confidential information is normally stored in a memory and a storage device of an information terminal device. Therefore to prevent the leakage of information, countermeasures must be taken for these memories.
As an example of such a countermeasure, an information processing device wherein data in memory is deleted when detachment of the memory is detected is disclosed (e.g. Japanese Patent Application Laid-Open No. 2002-73422).
Also a processing device, wherein a decoding key to read confidential data of a storage device is stored on another storage device, and the decoding key becomes invalid if the storage device storing the confidential data is removed, is disclosed (e.g. Japanese Patent Application Laid-Open No. H9-16477).
Also a computer, wherein the content of the memory is encrypted and written in memory just before power OFF, and is decoded when power is turned ON, so that the content of the memory, which is encrypted, cannot be viewed after power OFF, is disclosed (e.g. Japanese Patent Application Laid-Open No. 2001-202167).
Also an IC card, wherein the content of the memory is erased if the thin film battery is removed or the card itself is opened (e.g. Japanese Patent Application Laid-Open No. H11-328036, No. 2001-195307, and No. H10-320293), and a device with a safety information external access prevention function, wherein the content of the memory is reset if stress is applied to the piezo-electrical material (e.g. Japanese Patent Application Laid-Open No. H5-88986), are also available.
These prior arts, however, largely insure safety by erasing the content of a memory when the memory is removed from a device, and if a measurement device or an analyzer, such as a logic analyzer and oscilloscope for analyzing memory content, are used, the memory content can be analyzed without removing the memory.
Even if the content is encrypted at power OFF, it is still possible to analyze the content of the memory using such an analyzer during power ON.
Therefore according to these prior arts, the content of a memory, such as stored personal information, could be analyzed and stolen by an analyzer.